Populations of olfactory sensory neurons (OSNs) express hundreds of different olfactory receptors that participate in chemical detection as well as precise topographic mapping of sensory axons onto their postsynaptic targets in the olfactory bulb. The cAMP signaling pathway is critical to primary odor detection, but is only one of the signaling cascades activated by odorant receptors. Alternative pathways are likely to be involved in modulation of odorant detection or discrimination or perhaps in long term signaling of gene expression and in targeting of axons to specific glomeruli in the bulb. The biochemical mechanism of odorant receptor/transduction cascades cannot easily be studied in the complex array of olfactory neurons derived from intact animals. We will take advantage of an olfactory epithelium-derived cell line, odora, that can express functional olfactory receptors. This uniquely provides a reproducible and standardized source of material for biochemical and molecular analysis of the specificity and variety of the mechanisms of transduction. We will investigate whether individual receptors are able to interact with only one downstream transduction pathway or whether they are able to interact with multiple cascades as we hypothesize. We have identified phospholipase C (PLC) as the primary pathway for calcium influx activated by odorant in cells expressing odorant receptor U131. The pathway for calcium influx appears to be novel, and may provide insight into new mechanisms operating the olfactory system. We will investigate: 1)Which PLC pathway is activated by odorant receptor U131? 2) If it is activated through G proteins, which G protein is specifically activated? 3) Can a single receptor couple to two different pathways, activating both PLC and cAMP signaling? 4) Is pathway switching activated by cAMP or cAMP-dependent protein kinase? 5) Can these findings be generalized to other receptors (e.g., 17)? Future studies will explore whether these mechanisms of PLC signaling operate in OSNs in vivo and whether we have identified new signaling mechanisms that are likely to be generally true for many odorant receptors. The long term aim is to understand how odorant receptors couple to various signaling pathways. These insights are likely to be informative for more general questions of specificity of signaling, modulation of nerve activity and integration of information, and organization of cellular networks in the brain.